1. Field of the Invention
The present invention relates to an imager module for a camera, to a camera including such an imager module, and to a method for manufacturing the imager module.
2. Description of the Related Art
Such imager modules are used in particular in cameras for vehicles which are attached in the interior area of the vehicle and, for example, detect an exterior area outside the vehicle through a pane or also the interior area of the vehicle. The imager module is accommodated and contacted in a camera housing and may represent a finished, focused unit.
The imager module generally includes an objective holder, which may have a one-piece or also a multi-piece design and generally includes a tube area or a tubular area into which the objective is inserted in the longitudinal direction. The objective holder may have a multi-piece design and include a sensor carrier to which the tubular objective holder is attached; moreover, systems having a single-piece objective holder are also known, which thus has a carrier area for accommodating an image sensor and the tube area. The image sensor is mounted and contacted on the objective holder and together with the inserted objective defines the optical axis of the imager module. Image signals of the image sensor are read out by a control unit which is mounted on a circuit carrier board accommodated in the camera housing, for example.
The optical properties of the camera, i.e., in particular the focusing or focal length and possible malpositions, are thus established by inserting and mounting the objective in the objective holder.
In camera systems having fixed focusing (fixed-focus cameras), the objective is accommodated in the objective holder, focused once along the axis of symmetry of the tube area and then permanently fixed, for example with the aid of a bonded joint or an adhesive bond. The rear lens space between the last lens and the image sensor should preferably be free from disruptive particles. The positioning of the objective in the objective holder, and thus with respect to the image sensor, should have a preferably precise position in the longitudinal direction of the axis of symmetry of the tube area and in the clamping plane perpendicular thereto, and moreover should have a very precise orientation in the three spatial angles. Very precise focusing and positioning are required in particular for stereo camera systems for measuring distances.
For this purpose, generally different types of fixation with the aid of adhesive or frictional engagement are known. On the one hand, there are press fit joints, e.g., with the aid of press ribs extending in the longitudinal direction on the outer side of the objective and suitable mating surfaces in the objective holder. During insertion of the objective, the objective is thus pressed with its outer side and the press ribs formed on the outer side against the inner surface of the objective holder, whereupon a fixating glued joint may be created by introducing an adhesive. The orientation thus already takes place when the objective is pressed into the objective holder.
The disadvantage of such systems is that, in the case of the press fit joint, particles may be abraded from the press ribs, which may then fall into the rear lens space in a disruptive manner and end up on the image sensor, whereby the image quality may be considerably impaired. In particular, focusing by sliding the objective back and forth in the objective holder results in great particle abrasion. Moreover, depending on the tolerance situation, the press fit in part introduces great forces into the objective and the tube area of the objective holder.
Further known embodiments provide for a fixation of the objective in the objective holder with the aid of a clamping action between the inner surface of the objective holder and the outer surface of the objective by ascending or descending surfaces in the circumferential direction, e.g., as a wedge action. However, the disadvantage of such systems is that the two joining partners generally have complex surfaces; however, real surfaces generally deviate from the theoretical shape, so that the points of contact are often random, which may cause a negative impact on the precise position of the optical axis and the orientation in three spatial angles, i.e., a tilt of the optical axis of the objective with respect to the axis of the symmetry of the tube area.